program convex_polygon;

{$APPTYPE CONSOLE}

uses
  SysUtils;

var
  i, j, S0, S1, n : integer;
  x, y: array of integer;
  fin: textFile;

begin
  assignFile(fin, 'input.txt');
  reset(fin);
  read(fin, n);
  if (n=3) then
  begin
    write('this polygon is convex');
    j:=2;
  end;
  readln(fin);
  setlength(y, (n-(n div 2)));
  setlength(x, (n-(n div 2)));
  j:=0;
  for i:=0 to (2*n)-1 do
  begin
    if ((i mod 2)=0) then
    begin
      read(fin, x[j]);
      j:=j+1;
    end
    else
      read(fin, y[j-1]);
  end;
  i:=0;
  j:=1;
  while (j=1) do
  begin
    if (i<=n-4) then
    begin
      S0:=x[i]*y[i+1]-x[i+1]*y[i]+x[i+1]*y[i+2]-x[i+2]*y[i+1]+x[i+2]*y[i]-x[i]*y[i+2];
      i:=i+1;
      S1:=x[i]*y[i+1]-x[i+1]*y[i]+x[i+1]*y[i+2]-x[i+2]*y[i+1]+x[i+2]*y[i]-x[i]*y[i+2];
      if (S0*S1<0) then
      begin
        j:=2;
        write('this polygon is NOT convex');
      end;
    end
    else
    begin
      j:=2;
      write('this polygon is convex');
    end;
  end;
  readln;
end.
 